Journal of Neuroscience, Vol 8, 1194-1205, Copyright © 1988 by Society for Neuroscience
Development of ganglion cell topography in ferret retina
Z Henderson, BL Finlay and KC Wikler
University Laboratory of Physiology, Oxford University, UK.
The adult ferret has approximately 90,000 retinal ganglion cells, arranged
in a prominent area centralis and visual streak. The role of differential
cell generation, cell death, and retinal growth in the control of adult
retinal ganglion cell number and distribution was evaluated by examining
basic aspects of retinogenesis, including growth in retinal area,
developmental changes in the number, size, and distribution of retinal
ganglion cells (identification aided by retrograde transport of HRP), and
the incidence of degenerating cells in the ganglion cell layer. Retinal
development in the ferret was also compared to retinal development in the
cat (which has an even more differentiated area centralis) to determine
what alterations of developmental parameters are most closely associated
with this species difference in adult morphology. The area of the retina
increases linearly from birth (12 mm2) to postnatal day 24 (54 mm2),
reaching an eventual adult value of 64 mm2. Ganglion cell numbers peak at
155,000 (approximately twice the adult number) on postnatal day 3, and fall
to adult numbers by postnatal day 6. The remaining cells of the ganglion
cell layer, principally displaced amacrine cells, reach their peak number
on postnatal day 10 (approximately 280,000), falling to 200,000 by
adulthood. Degenerating cells are abundant in the ganglion cell layer in
the immediate postnatal period. A difference in the incidence of
degenerating cells in the presumptive area centralis versus that in the
retinal periphery was not observed postnatally, though there were other
striking spatial nonuniformities, suggesting that differential cell loss
might contribute to other features of retinal topographic organization.
Ganglion cell density is virtually uniform across the retina at birth. Cell
density is first reduced in the dorsal retina, resulting in a
dorsal-to-ventral gradient in cell density that persists until day 10, when
ganglion cell number has stabilized. By postnatal day 24, an area centralis
and visual streak has emerged, but not of adult magnitude. Because ganglion
cell number has stabilized long before the area centralis and visual streak
emerge, we conclude that differential retinal growth is the principal
mechanism producing this feature of retinal topography. Comparison with the
cat suggests that the proportionately greater nonuniform growth of the
cat's eye accounts for the greater differentiation of its area centralis.
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